Feeds:
Posts
Comments

Posts Tagged ‘biomechanics’

I still have my original photocopy, from my grad school days circa 1996, of the 1983 Ted Garland classic paper “The relation between maximal running speed and body mass in terrestrial mammals”, festooned with my comments and highlighter pen marks and other scribblings. That paper remains the backbone of many research questions I am interested in today, and I often think about its underlying concepts. Here’s the key scatterplot from that paper, which I could almost replot by hand from memory, it is so full of implications (and can be clicked to embiggen it, perhaps even speedily depending on your internet connection):

Garland 1983- max speed

Stomach-Churning Rating: 1/10; data and their ramifications; offal-free.

The major points (IMO there are less exciting ones about which theoretical scaling model the data best fit) of the paper are: (1) the fastest-running mammals are neither the smallest nor largest, but those around ~100 kg body mass; (2) if you fit a linear equation to the data (see above; hashed line), it seems like speed increases with body mass linearly (with no limit to that increase, within the body mass range of the data), but if you analyze individual groups of mammals they either don’t change speed significantly with size or they get slower– refer back to point #1 and the polynomial regression that is shown in the figure above (curved line). That’s the biological-question-driven science at the core of the paper (with some methods-y questions at their foundation; e.g. should we use a linear or polynomial regression to fit the data? The latter fits best, and gives a different answer from the former, so it matters.).

But what also fascinates me is the question of data. As the author, who taught me Evolution as an undergrad at U Wisconsin (this had a big impact on me), fully admits in the paper, the ~3-page table of data “necessarily sacrifices some accuracy for completeness”. This paper is about a big question, how mammal speed changes with size, and so its big question explicitly allows for some slop in the data (I will return to this issue of slop later). But given that very few of the data points have very accurate measurements for speed, or for body mass for that matter, how much can we trust an x-y plot of those data, no matter what method is used? Oh there is so much opportunity here for geeky pedantry and niggling scrutiny of data points, true, but hold on…

Plenty of follow-up papers have mused over that latter question, and spin-off ones. Here are some of their plots, re-analyzing the same or very similar data in different contexts. A look at how these papers examine these data and related questions/methods leads into some avenues of science that fascinate me:

Garland 1988- max perf

Garland and Baudinette (link to pdf here) checked whether placental (i.e. most; including us) mammals could run/hop faster than marsupial (pouched; e.g. kangaroos) mammals. Their results said “not really”, as the plot intimates. Scatter in the data, especially between 0.01-10 kg, confounds the issue- there’s a lot of specialization going on (notably, animals that are very slow for their size, e.g. sloths). But marsupials are not, as had been suggested before, inferior to placentals in some basic way such as running ability.

GarlandJanis1993-Fig5

Above, Garland and Janis 1993 (link to pdf here) examined how the ratio of metatarsal (“sole bones” of the lower end of the leg/foot) vs. femur (thigh bone) length relate to speed, with evolutionary relationships taken into account. The methods (“independent contrasts” and its conceptual kin; I won’t delve into that morass more here!) did not exist for looking at phylogeny’s effects on the results in Garland’s 1983 paper. Yet “cursoriality” (relative elongation of the lower limb) had been thought to relate to running speed for over 80 years at that time, so that was what they tested: how much does limb-elongation correlate in a positive way with maximal running speed? They found that the answer was “sort of”, but that other things like home range size, energetics, ecology, etc. might explain as much/more, so caveat emptor. And by looking at the plot above, it’s evident that there’s a lot of specialization (scatter, along the x and/or y axes– check out the giraffe/Giraffa and cheetah/Acinonyx outliers, for example). While ungulates seemed to have a better relationship of speed and limb dimensions, their predatory carnivoran relatives did not.Christiansen 2002- max speed

Christiansen was one of two studies in 2002 that looked back on those Garland 1983 data in a new way, and like the 1993 study with Janis considered these data in light of limb lengths too.  The plot above delved into how running speed changes with lengths of forelimb bones, again finding appreciable curvilinearity (indirectly supporting the non-linear scaling idea– even at large sizes, relatively longer-legged mammals aren’t faster). The plot on the right side (b) measured the relative length of the olecranon process; the “funny bone” that acts as a lever for support of the elbow joint against gravity. Again, even mammals that have stouter elbow-supporting processes aren’t faster; there’s a “happy medium” of elbow-osity for optimizing running speed (and huge scatter in the data!). Ultimately, this analysis concluded that it wasn’t speed that animal anatomy seemed to be optimizing overall, especially as size increased, but rather energetic cost, although there was a lot of variation in the data and accounting for phylogeny only muddled things up more (as it tends to do).

diaz2002

Iriarte-Diaz was the other 2002 study to tackle the speed-vs-size issue. It focused primarily on whether mammal speeds showed “differential” (i.e. non-linear) scaling with size, as per the polynomial regression in Garland’s 1983 study. It showed that smaller mammals seemed to either get slightly slower with increasing size or else not change maximal speed (depending on detailed methods/data stuff that don’t matter here), whereas bigger mammals exhibited very strong declines of speed with size past a threshold (optimal) body mass.

So, repeated analyses of Garland’s 1983 data (and modifications of those data) at least uphold the fundamental conclusion that big land mammals cannot move quickly, in an absolute sense (meters/sec or kph or mph) — and much more so in a relative sense (e.g. body lengths/second or other normalized metrics). We might then ask why, and my research scrutinizes this issue in terms of the fundamental mechanisms of movement biomechanics and anatomy that might help to explain why, but for brevity I won’t go there in this post. I want to wander elsewhere.

I want to wander back to those data used in the above (and other) studies. All of the studies discuss the quality of the data and bemoan the lack of quality. I’d agree with them that it’s hard to imagine most of the data being consistently off in a biased way that would fundamentally alter their conclusions. But I still worry. We should worry about the data points for the extreme animals- the fastest, slowest, largest and smallest. We should worry about subjectively removing “outliers” such as hippos or cheetahs, as they do change some of the results.

I worry about elephants, for example: my work has shown that they can “run” about 7 meters/second or ~25 kph; not the 35 kph used as data for African elephants (from speedometer-y anecdotal estimates)– ~1.4 times the speed we’ve been able to measure for both species. And are a white rhino and hippo able to run at this same 25 kph speed as the original data in the 1983 study state, or faster/slower? No one has really nicely measured this so we can’t be sure, but I can imagine it being off by a similar 40% or so. On the other hand, if the bigger animals in the dataset are slower than the original data, that actually strengthens the conclusion that bigger animals are slower, so who cares that much, in the grand scheme of things?

We could worry about plenty of other maximal speed data points, and the “average” adult body masses assumed (although I doubt those would change the results as much as the speed errors). Maybe another question is, in doing such broad-scale analyses should we only include data points that have maximal precision (e.g. elephants, horses, cheetahs, greyhounds, humans and a few others)? We’d maybe be able to do a study of 20 or so species. I doubt it would show much that is different if we did, although I expect that sample size and noise would begin to dampen out the signal. See below.

However, a double standard begins to become evident here. In modern biomechanics (and probably the rest of biology/science), there’s a strong emphasis on data quality and technologically precise measurement. Garland’s 1983 study might be hard to get past peer review today (or maybe not). We agonize over single-species studies trying hard to measure animals’ maximal speeds (a very hard thing to be sure of in terms of motivation, but not intractable unless one takes an almost antiscientific/overly cynical view that animals could always be holding back some critical reserve unless they run for their lives– is that reserve 1%, 10% or 100%? Probably closer to the middle, in good studies). We measure multiple animals and many trials, in field and/or lab conditions, with documented video footage at high resolution and frame rate, with GPS tracking or other tools to maximize precision. We take pride in these high standards today. That’s what makes scientists wriggle uncomfortably when we look back at the data in those older maximal speed papers and ponder how few data points are verified, documented, precise and essentially trustworthy.

So should broad studies be working by the same standards as narrow studies? (I’m far, far, far from the first scientist to think about this but it’s interesting for me at least to think about it in this case and others) There is potential tension here between empiricists who want precise data and theoreticians who want to tackle those Big Questions, and that’s a pattern one can see throughout much of science. I sit on the fence myself, doing both approaches. I can think of plenty of similar examples, in “big data” palaeobiology, morphometrics, genomics, physics and so on. Some of those fields have nice databases with quality control over the data; they’ve maybe solved this problem to a large degree. This tiny area of mammalian maximal speeds hasn’t solved it, but how urgent is the need to?

On the flip side, even if the data points have some error of 10-20% or even 40% that error will probably be largely random, not biased toward assuming that bigger or smaller animals are slower than they truly are, or medium-sized animals faster. We still have the reliable cheetah data point (and racehorses, and greyhounds) showing >100 kph (and 70 kph) speeds for ~100 (and ~40, 400ish) kg animals, so there is evidence for a peak of maximal speed (the cheetah outlier, and one might also throw in pronghorn antelope or others that are pretty damn fast but not yet well measured) at medium body size. I expect there would be incremental overall progress if we did improve the data quality, and that would still be nice (comforting!) but it would be a tough, tough slog. Indeed, my team is doing its share of that, already tackling the data point for giraffes this year (stay tuned!). The potential gains are still there, especially for understanding the unique biology of individual species– that noise in the data (or specialization, if you prefer) is interesting!!! We need that kind of work, partly because the big questions, sexy as they are, still depend on having data quality as a foundation, and old questions still need revisiting from time to time as data quality is improved by those in the trenches of gathering it.

My team’s journal club has gone over the Garland paper lately and we’re hitting the others later this summer, but I wanted to throw these thoughts out there on this blog now to see if they generated any fun discussion, or they might introduce others to the science of maximal speeds and what we do/don’t know. One thing we don’t know much about is what kinds of patterns non-mammalian groups exhibit today. Chris Clemente did some great work on this with lizards, finding a pattern similar to the mammal one. I’ve struggled in my work to move toward trying to address similar questions for extinct groups, but there the data quality presents a challenge I find exciting rather than depressing, although I still have to shrug when I see limb lengths or proportions being used as a proxy for speed. We can do better.

So I’d love to hear your thoughts on any of the points here. Maybe some of the old-timers have stories from ye olden days when Garland’s work was originally published; I’d love to hear those, or other points/questions/favourite papers.

Read Full Post »

Who needs “Ice Road Truckers” when you have the “John’s Freezer” team on the road with fossils, amphibians, felids and 3D phenotype fun? No one, that’s who. We’re rocking the Cheltenham Science Festival for our first time (as a group), and pulling out all the stops by presenting two events! Here’s the skinny on them, with updates as the week proceeds.

Stomach-Churning Rating: 2/10 for now (just bones), but it could change once the cheetah dissection is under way… 8/10 bloody cheetah bits but only at the end (updated)

Right now, Lauren Sumner-Rooney (of “Anatomy To You” and other fame) is on-site with a rotating team of others from our lab, in the “Free Activity Tents” area of the Imperial Gardens/Square, inside a marquee where we’ll be showing off our NERC-funded tetrapod research all week. This “First Steps” event features not only our past and present work with Jenny Clack, Stephanie Pierce, Julia Molnar and others on Ichthyostega & its “fishapod” mates, but also our “scampering salamanders” research in Spain, Germany and England. I’ve blogged a lot about all that, and won’t repeat it here, but you can see a 3D-printed Ichthyostega skeleton, view the skeleton in a virtual reality 3D environment, see related specimens and engage in kid-friendly activities, and talk to our team about this and other related research.

Ichthyostega 3D printed backbone is born!

Ichthyostega 3D printed backbone is born!

The central themes of that event are how bone structure relates to function and how we can use such information, along with experimental measurements and computer models of real salamanders, to reconstruct how extinct animals might have behaved as well as how swimming animals became walking ones. How did fins transform into limbs and what did that mean for how vertebrates made the evolutionary transition onto land? If you know my team’s work, that encapsulates our general approach to many other problems in evolutionary biomechanics (e.g. how did avian bipedalism evolve?). Added benefits are that you too can explore this theme in a hands-on way, and you can talk with us about it in person. That continues all week (i.e. until Saturday evening); I’ll be around from Thursday afternoon onwards, too. Kids of all ages are welcome!

Ichthyostega 3D print taking shape!

Ichthyostega 3D print taking shape!

Then, on Saturday for our second free event we join forces with Ben Garrod (master of primate evolution, the secrets of bones, and “Attenborough and the Giant Dinosaur”) and RVC’s forensic pathologist Alexander Stoll as well as Sophie Regnault (“sesamoid street” PhD student w/me). As the “Large Animal Dissection” title hints, it’s not the right kind of gig to bring small kids to. There will be blood and stuff— we’ll be dissecting a cheetah together from 10am-4pm. This will involve walking through all the major organ systems, giving evolutionary anecdotes, and plenty more, with an aim to understand how the magnificent adaptations of cheetahs evolved—but also to investigate what problem(s) this animal faced that led to its sad demise. By the day’s end, there will just be a skeleton left. Get a front row seat early for this event, which serendipitously ties into “Team Cat”’s Leverhulme Trust-funded research project (we wanted a big animal and it just happened to be a cheetah; I had hoped for a giant croc or a shark or something but can’t complain!).

Ichthyostega 3D print is ready!

Ichthyostega 3D print is ready!

If you miss these events, please do cry bitter tears of regret. But don’t despair, there will be another “big cat dissection” in the London area in ~November (watch here for details), and plenty more fossil tetrapod stuff to come, plus a LOT more dinosaurs on the horizon!

Guess the bones! (photo by Zoe Self)

Guess the bones! (photo by Zoe Self)

And please come back to this blog post for more pics and stories as the week carries on… For hashtag afficionados, you can follow the fun on Twitter etc. at #firststepsCSF16. What a world we live in!

Update 1: While you’re here, check out our Youtube playlists of tetrapod-related videos:

Lobe-finned fishes

Ichthyostega‘s awesome anatomy

Tetrapod evolution: Tiktaalik to salamanders!

Update 2: Photos of our main stand (about tetrapod evolution)

csf2016-display

Our poster/banner display looks nice.

20160609_143548

Our tent brings in some punters.

20160609_151508

Our bones excite people young and old, sighted and blind.

20160610_090009

Fun with stickers and lab t-shirts.

And…

Update 3: Cheetah meat & greet
Ben, Alex, Sophie and I tackled the cheetah dissection today and it went GREAT! Much better than I’d optimistically expected. Rain didn’t scare the crowds off and neither did the gore, which there was some of (gelatinous spinal cords, lumpy tumors and at least one flying tiny bit of cheetah flesh that landed on a good-natured audience member!). Photos will tell the tale:

20160611_091345

Peek-a-boo!

20160611_093828

Sophie and Alex help us get set up in our tent.

20160611_094554

Our initial rough schedule- although we ended up improvising more after lunch.

20160611_095500

Dissectors assemble!

20160611_105126

The beast revealed. It was skinned by the museum that loaned it to us.

20160611_110748

Alex showing his talent: removing the viscera in one piece from end to end, starting with the tongue.

20160611_153148

Impressive finding of a surgical fixture (plate and wires) on the tibia, which had been used to hold the shattered bone back together long enough for it to heal. Added to the kidney disease and liver-spleen-lung cancer, this cheetah was in the sorriest shape of any cadaver I’ve seen yet.

20160611_153213

Cheetah coming to pieces: (from bottom) lumbar/pelvic region, hindlimb, thorax, forelimb and other bits.

20160611_155452

Dr Adam Rutherford, an eye expert, did a nice dissection of the cheetah’s eye, here showing the tapetum lucidum (reflective membrane), which shows up as light blue colour. Its small size befits the not-very-nocturnal habits of cheetahs.

20160611_155459

The lens of the cheetah’s eye. Now cloudy because of dehydration and crystalization, but still fascinating to see.

Want to see more images and the enthusiastic responses from the audience (we got some great feedback)? Check out Twitter’s #cheltscifest feed, or more simply my Storify condensation of the cheetah-related tweets here.

Read Full Post »

Last year we finally, after about 14 years of slow work, released our biomechanical model of an ostrich’s hindleg. We showed how it informed us about the potential leverages (moment arms; contributions to mechanical advantage of the joints) of all of the muscles. It was a satisfying moment, to understate it, to finally publish this work from my postdoc at Stanford. Today, we begin to deliver on that model’s promise. And it only took 4 years or so, roughly? The journal Royal Society Interface has published our study of how we used this musculoskeletal model to simulate walking and running dynamics. Those simulations join an intimidatingly broad and complex literature using similar models to study human (and some other primate) locomotion or other functions at the level of individual muscles (for whole limbs/bodies) in vast detail and growing rigor. I have Dr. Jeffery Rankin, a research fellow finishing up his post with me after ~6 years of hard work on many projects, to thank for driving this work forward, and Dr. Jonas Rubenson (now at PennState) for his patient collaboration that has continued since the early 2000’s.

Stomach-Churning Rating: 2/10; computer models of muscle actions. The underlying anatomical data are goopy, as prior ostrich-dissection-focused posts show!

Our model; in right side view (on the left) and frontal view (on the right), with muscles in red and the leg's force as the blue arrow; frozen at the middle of a step.

Our model; in right side view (on the left) and frontal view (on the right), with muscles in red and the leg’s force as the blue arrow; frozen at the middle of a running step.

Simulations like these predict things that we can’t easily measure in living animals, such as how much force muscles and tendons generate, how quickly those tissues change length, how much mechanical energy they thus contribute to the joints, limbs and whole body, how much metabolic energy their actions cost, and much more. There are more ways to use these tools than I have space or time to explain, but simply put we forced our ostrich simulation to match experimental measurements of the motions and forces of a representative walking and running ostrich stride, from contact of one foot until the next time that foot hit the ground. It then used optimization methods (minimizing target criteria like muscle stress) to estimate how the muscles and tendons were used to generate those motions and forces. This is a ways ahead of some prior ostrich simulations such as this one that I recall from classes during my PhD studies.

Any modeller worth their salt knows that their models and simulations are wrong at some level. This is much as most science is “wrong”; i.e. a simplification of reality with some errors/noise introduced by assumptions, variation, methods and such. But generally these kinds of musculoskeletal dynamic simulations hold up pretty well against experimental data. A standard “validation” is to test how closely the simulations’ predictions of muscle activity match the “real” (measured in life, also with some uncertain error) activity of muscles. Science still lacks those data for ostriches, but fortunately measurements from other birds (by Steve Gatesy and colleagues) indicate that muscles tend to follow fairly conservative patterns. Grossly speaking, avian leg muscles tend to either be active mainly when the foot is on the ground (stance phase) or off the ground (swing phase). Some studies acknowledge that this is an oversimplification and other muscles do act across those two phases of a stride, either in multiple pulses or as “transitional” (stance-to-swing or swing-to-stance) switch-hitters in their activations. Our ostrich predictions matched the qualitative patterns for avian muscle activations measured to date, so that’s good. The results also reinforced the notion of transitional or multi-phasic muscle activation as still having some importance, which bears more study.

Yet what did the simulations with our ostrich model tell us that other ostrich experiments or other bird species didn’t? Three main things. First, we could calculate what the primary functions of muscles were; they can act as motors (generating energy), brakes (absorbing energy), springs (bouncing energy back and forth) or struts (just transmitting force). We could then sum up what whole muscle groups were doing overall. The image below shows how these broad functions of groups vary across the stance phase (swing phase is harder to condense here so I’ve left it out).

Positive work can speed things up; negative work can slow things down.

Positive work can speed things up; negative work can slow things down. Solid bars are running; striped bars are walking. (from our Fig. 13) You may need to click to em-broaden this image for the gory biomechanical details.

There’s a lot going on there but a few highlights from that plot are that the hip extensor (antigravity) muscles (biarticular hip/knee “hamstrings”) are acting like motors, the knee extensors (like our quadriceps) are mainly braking as in other animals and the ankle is fairly springy as its tendons (e.g. digital flexors; gastrocnemius) suggest. We often characterize birds as “knee-driven” but it’s more accurate biomechanically to say that their hips drive (power; i.e. act as motors) their motion, whereas their knees still act as brakes — in both cases as in many other land vertebrates. Thus in some ways bird legs don’t work so unusually. Birds like ostriches are, though, a little odd in how much they rely on their hamstring muscles to power locomotion (at the hip) rather than their caudofemoral muscles, which are reduced. Zooming in on some particular muscles such as parts of the hip or knee extensors, the functions sometimes weren’t as predictable as their similar anatomy might suggest. Some muscles had parts that turned on during swing phase and other parts used during stance phase. Neural control and mechanics can produce some unexpected patterns.

Second, we looked at one important methodological issue. Simulations of musculoskeletal dynamics can vary from simple static (assuming each instant of a motion is independent from the others; e.g. ignoring acceleration, inertia, tendon effects, etc.) to more complex grades of fully dynamic flavours (e.g. assuming rigid or flexible tendons). We looked across this spectrum of assumptions, for both walking and running gaits, with the expectation that more static assumptions would work less well (vs. more dynamic ones; by various criteria) for running vs. walking. This also showed us how much tendons influence our simulations’ estimates of muscle mechanics—a fully rigid tendon will make the muscle do all of the work (force times length change) whereas a flexible tendon can literally take up some (or even all) of that slack, allowing muscles to remain closer to their isometric (high force-generating, negligible length change) quasi-optimum.

Nicely, our predicted muscle functions weren’t influenced much by these methodological variations. However, static assumptions  clearly were in some ways less appropriate for running than for walking, as were flexible tendons. Somewhat surprisingly, making the simulations more dynamic didn’t lower the levels of activation (and thus presumably the metabolic costs) of muscles, but actually raised those levels. There are good reasons why this might be realistic but it needs further study. It does muddy the waters for the issue of whether assuming that rapid locomotion can be modelled as static is a “bad” thing such as for estimating maximal speeds—yes, tendons can do more (elastic energy storage, etc.) if more dynamic models are used, but co-contraction of antagonistic muscles against each other also brings in some added costs and might lead to slower speed estimates. We’ll see in future work…

Finally, one often overlooked (sometimes even undiscussed!) aspect of these simulations is that they may silently add in extra forces to help muscles that are struggling to support and move their joints. The justification is typically that these extra “reserve actuators” are passive tissues, bony articular forces and other non-muscular interactions. We found that the hip joint muscles of ostriches were very weak at resisting abduction (drawing the thigh away from the body) and this needed resisting during the stance phase, so our simulations had very high reserve actuators switched on there. That fits the anatomy pretty well and needs more investigation.

Want to know more? Happily, not only is the paper free for anyone to view but so are all of the data including the models (modified slightly from our last paper’s). So, although the software (Opensim) isn’t ideal for 4-year-olds to play with (it is fancy engineering stuff), if you have the interest and dilligence it is there to play with and re-use and all that. But also watch this space for future developments, as there is more to happen with our steadily improving models of ostriches and other beasties. Anyway, while this paper is very technical and challenging to explain I am not too bashful to say it’s one of the finer papers from my career; a big stride forward from what we’ve done before. I have been looking forward for a long time to us getting this paper out.

P.S. Our peer reviewers were splendid- tough but constructive and fair. The paper got a lot better thanks to them.

Read Full Post »

Deck the ‘Nets With PeerJ Papers— please sing along!

♬Deck the ‘nets with PeerJ papers,
Fa la la la la, la la la la.
‘Tis the day to show our labours,
Fa la la la la, la la la la.

Downloads free; CC-BY license,
Fa la la, la la la, la la la.
Read the extant ratite science,
Fa la la la la, la la la la.

See the emu legs before you
Fa la la la la, la la la la.
Muscles allometric’ly grew.
Fa la la la la, la la la la.

Follow the evolvin’ kneecaps
Fa la la la la, la la la la.
While we dish out ratite recaps 
Fa la la la la, la la la la.

Soon ostrich patellar printing
Fa la la la la, la la la la.
Hail anat’my, don’t be squinting
Fa la la la la, la la la la.

Dissections done all together
Fa la la la la, la la la la.
Heedless of the flying feathers,
Fa la la la la, la la la la♪

(alternate rockin’ instrumental version)

Stomach-Churning Rating: 5/10: cheesy songs vs. fatty chunks of tissue; there are no better Crimbo treats!

Today is a special day for palaeognath publications, principally pertaining to the plethora of published PeerJ papers (well, three of them anyway) released today, featuring my team’s research! An early Crimbo comes this year in the form of three related studies of hind limb anatomy, development, evolution and biomechanics in those flightless feathered freaks of evolutionary whimsy, the ratites! And since the papers are all published online in PeerJ (gold open access), they are free for anyone with internet access to download and use with due credit. These papers include some stunning images of morphology and histology, evolutionary diagrams, and a special treat to be revealed below. Here I’ll summarize the papers we have written together (with thanks to Leverhulme Trust funding!):

1) Lamas, L., Main, R.P., Hutchinson, J.R. 2014. Ontogenetic scaling patterns and functional anatomy of the pelvic limb musculature in emus (Dromaius novaehollandiae). PeerJ 2:e716 http://dx.doi.org/10.7717/peerj.716 

My final year PhD student and “emu whisperer” Luis Lamas has published his first paper with co-supervisor Russ Main and I. Our paper beautifully illustrates the gross anatomy of the leg muscles of emus, and then uses exhaustive measurements (about 6524 of them, all done manually!) of muscle architecture (masses, lengths, etc.) to show how each of the 34 muscles and their tendons grew across a more than tenfold range of body mass (from 6 weeks to 18 months of age). We learned that these muscles get relatively, not just absolutely, larger as emus grow, and their force-generating ability increases almost as strongly, whereas their tendons tend to grow less quickly. As a result, baby emus have only about 22% of their body mass as leg muscles, vs. about 30% in adults. However, baby emus still are extremely athletic, more so than adults and perhaps even “overbuilt” in some ways.

This pattern of rapidly growing, enlarged leg muscles seems to be a general, ancestral pattern for living bird species, reflecting the precocial (more independent, less nest-bound), cursorial (long-legged, running-adapted) natural history and anatomy, considering other studies of ostriches, rheas, chickens and other species close to the root of the avian family tree. But because emus, like other ratites, invest more of their body mass into leg muscles, they can carry out this precocial growth strategy to a greater extreme than flying birds, trading flight prowess away for enhanced running ability. This paper adds another important dataset to the oft-neglected area of “ontogenetic scaling” of the musculoskeletal system, or how the locomotor apparatus adapts to size-/age-related functional/developmental demands as it grows. Luis did a huge amount of work for this paper, leading arduous dissections and analysis of a complex dataset.

Superficial layer of leg muscles in an emu, in right side view.

Superficial layer of leg muscles in an emu, in right side view. Click any image here to emu-biggen. The ILPO and IC are like human rectus femoris (“quads”); ILFB like our biceps femoris (“hams”); FL, GM and GL much like our fibularis longus and gastrocnemius (calf) muscles, but much much bigger! Or, perhaps FL stands for fa la la la la?

Data for an extra set of emus studied by coauthor Russ Main in the USA, which grew their muscles similarly to our UK group. The exponents (y-axis) show how much more strongly the muscles grown than isometry (maintaining the same relative size), which is the dotted line at 1.0.

Data for an extra set of emus studied by coauthor Russ Main in the USA, which grew their muscles similarly to our UK group. The exponents (y-axis) show how much more strongly the muscles grew than isometry (maintaining the same relative size), which is the dotted line at 1. The numbers above each data point are the # of individuals measured. Muscle names are partly above; the rest are in the paper. If you want to know them, we might have been separated at birth!

2) Regnault, S., Pitsillides, A.A., Hutchinson, J.R. 2014. Structure, ontogeny and evolution of the patellar tendon in emus (Dromaius novaehollandiae) and other palaeognath birds. PeerJ 2:e711 http://dx.doi.org/10.7717/peerj.711

My second year PhD student Sophie Regnault (guest-blogger here before with her rhino feet post) has released her first PhD paper, on the evolution of kneecaps (patellae) in birds, with a focus on the strangeness of the region that should contain the patella in emus. This is a great new collaboration combining her expertise in all aspects of the research with coauthor Prof. Andy Pitsillides‘s on tissue histology and mine on evolution and morphology. This work stems from my own research fellowship on the evolution of the patella in birds, but Sophie has taken it in a bold new direction. First, we realized that emus don’t have a patella– they just keep that region of the knee extensor (~human quadriceps muscle) tendon as a fatty, fibrous tissue throughout growth, showing no signs of forming a bony patella like other birds do. This still blows my mind! Why they do this, we can only speculate meekly about so far. Then, we surveyed other ratites and related birds to see just how unusual the condition in emus was. We discovered, by mapping the form of the patella across an avian family tree, that this fatty tendon seems to be a thing that some ratites (emus, cassowaries and probably the extinct giant moas) do, whereas ostriches go the opposite direction and develop a giant double-boned kneecap in each knee (see below), whereas some other relatives like tinamous and kiwis develop a more “normal”, simple flake-like bit of bone, which is likely the state that the most recent common ancestor of all living birds had.

There’s a lot in this paper for anatomists, biomechanists, palaeontologists, ornithologists, evo-devo folks and more… plenty of food for thought. The paper hearkens back to my 2002 study of the evolution of leg tendons in tetrapods on the lineage that led to birds. In that study I sort of punted on the question of how a patella evolved in birds, because I didn’t quite understand that wonderful little sesamoid bone. And now, 12 years later, we do understand it, at least within the deepest branches of living birds. What happened further up the tree, in later branches, remains a big open subject. It’s clear there were some remarkable changes, such as enormous patellae in diving birds (which the Cretaceous Hesperornis did to an extreme) or losses in other birds (e.g., by some accounts, puffins… I am skeptical)– but curiously, patellae that are not lost in some other birds that you might expect (e.g., the very non-leggy hummingbirds).

Fatty knee extensor tendon of emus, lacking a patella. The fatty tissue is split into superficial (Sup) and deep regions, with a pad corresponding to the fat pad in other birds continuous with it and the knee joint meniscus (cushioning pad). The triceps femoris (knee extensor) muscle group inserts right into the fatty tendon, continuing over it. A is a schematic; B is a dissection.

Fatty knee extensor tendon of an emu, showing the absence of a patella. The fatty tissue is split into superficial (Sup) and deep regions, with a pad corresponding to the fat pad in other birds continuous with it and the knee joint meniscus (cushioning pad). The triceps femoris (knee extensor) muscle group inserts right into the fatty tendon, continuing on over it. A is a schematic; B is a dissection.

Sectioning of a Southern Cassowary's knee extensor tendon, showing: A Similar section  as in the emu image above. revealing similar regions and fibrous tissue (arrow), with no patella, just fat; and B, with collagen fibre bundles (col), fat cells (a), and cartilage-like tissue (open arrows) labelled.

Sectioning of a Southern Cassowary’s knee extensor tendon, showing: A, Similar section as in the emu image above. revealing similar regions and fibrous tissue (arrow), with no patella, just fat; and B, With collagen fibre bundles (col), fat cells (a), and cartilage-like tissue (open arrows) labelled.

Evolution of patellar form in birds. White branches indicate no patella, blue is a small flake of bone for a patella, green is something bigger, yellow is a double-patella in ostriches, and grey is uncertain. Note the uncertainty and convergent evolution of the patella in ratite birds, which is remarkable but fits well with their likely convergent evolution of flightlessness and running adaptations.

Evolution of patellar form in birds. White branches indicate no patella, blue is a small flake of bone for a patella, green is something bigger, yellow is a double-patella in ostriches, black is a gigantic spar of bone in extinct Hesperornis and relatives, and grey is uncertain. Note the uncertainty and convergent evolution of the patella in ratite birds (Struthio down to Apteryx), which is remarkable but fits well with their likely convergent evolution of flightlessness and running adaptations.

3) Chadwick, K.P., Regnault, S., Allen, V., Hutchinson, J.R. 2014. Three-dimensional anatomy of the ostrich (Struthio camelus) knee joint. PeerJ 2:e706 http://dx.doi.org/10.7717/peerj.706

Finally, Kyle Chadwick came from the USA to do a technician post and also part-time Masters degree with me on our sesamoid grant, and proved himself so apt at research that he published a paper just ~3 months into that work! Vivian Allen (now a postdoc on our sesamoid bone grant) joined us in this work, along with Sophie Regnault. We conceived of this paper as fulfilling a need to explain how the major tissues of the knee joint in ostriches, which surround the double-patella noted above, all relate to each other and especially to the patellae. We CT and MRI scanned several ostrich knees and Kyle made a 3D model of a representative subject’s anatomy, which agrees well with the scattered reports of ostrich knee/patellar morphology in the literature but clarifies the complex relationships of all the key organs for the first time.

This ostrich knee model also takes Kyle on an important first step in his Masters research, which is analyzing how this morphology would interact with the potential loads on the patellae. Sesamoid bones like the patella are famously responsive to mechanical loads, so by studying this interaction in ostrich knees, along with other studies of various species with and without patellae, we hope to use to understand why some species evolved patellae (some birds, mammals and lizards; multiple times) and why some never did (most other species, including amphibians, turtles, crocodiles and dinosaurs). And, excitingly for those of you paying attention, this paper includes links to STL format 3D graphics so you can print your own ostrich knees, and a 3D pdf so you can interactively inspect the anatomy yourself!

(A) X-ray of an ostrich knee in side view, and (B) labelled schematic of the same.

Ostrich knee in side view: A, X-ray, and (B) labelled schematic.

3D model of an ostrich knee, showing: A, view looking down onto the top of the tibia (shank), with the major collateral ligaments (CL), and B, view looking straight at the front of the knee joint, with major organs of interest near the patella, sans muscles.

3D model of an ostrich knee, showing: A, View looking down onto the top of the tibia (shank), with the major collateral ligaments (CL), and B, View looking straight at the front of the knee joint, with major organs of interest near the patella, sans muscles.

You can view all the peer review history of the papers if you want, and that prompts me to comment that, as usual at PeerJ (full disclosure: I’m an associate editor but that brings me £0 conflict of interest), the peer review quality was as rigorous at a typical specialist journal, and faster reviewing+editing+production than any other journal I’ve experienced. Publishing there truly is fun!

Merry Christmas and Happy Holidays — and good Ratite-tidings to all!

And stay tuned- the New Year will bring at least three more papers from us on this subject of ratite locomotion and musculoskeletal anatomy!

♬Should auld palaeognathans be forgot, 
And never brought for scans? 
Should publications be soon sought, 
For auld ratite fans!♪

Read Full Post »

Title says it all? Sometimes a spade needs to be called a spade.

From time to time the Structure & Motion Lab at the RVC gets cool videos of animals doing different behaviours, be that slow-mo/high-speed videos, x-ray videos. motion capture or whatever. Actually, we get cool videos pretty much every day but some of them (such as a racehorse galloping on a treadmill) seem mundane to us, much as our visitors are impressed.

Here are some examples of the stuff we’ve filmed recently. It all seems to belong on this blog as an example of anatomy in motion, but has no good home here otherwise and no other cohesive threads uniting the disparate videos.

Hence the title. Enjoy!

The above two videos were made by Renate Weller, Emily Sparkes and others. Looping GIF of the last one, via Marko Bosscher:

X-Ray_Hamster

Shin-Ichi Fujiwara, myself and others made that video some years ago; research yet to be finished.

The above two high-speed videos were captured many moons ago with Alexis Wiktorowicz, Karin Jespers and others; more research yet to be finished.

Ashley Heers made this video for the “Fossil Wonderlands” documentary in 2013-14.

Check us out on BBC2 tonight in Cat Watch, with more videos!

 

Read Full Post »

[This is the original, unedited text of my shorter, tighter (and I think actually better) News & Views piece for Nature, on the paper described below)

Ambitious experimental and morphological studies of a modern fish show how a flexible phenotype may have helped early “fishapods” to make the long transition from finned aquatic animals into tetrapods able to walk on land.

Stomach-Churning Rating: 1/10. Cute fish. Good science. Happy stomachs!

Photo by Antoine Morin, showing Polypterus on land.

Photo by Antoine Morin, showing Polypterus on land.

Napoleon Bonaparte’s military excursions into Egypt in 1798-1799 led a young French naturalist, Ètienne Geoffroy Saint-Hilaire, to cross paths with a strange fish that had paired lungs and could “walk” across land on its stubby, lobelike fins. In 1802, he dubbed this fish “Polyptère bichir”1, today known as the Nile bichir, Polypterus bichir La Cepède 1803. The bichir’s mélange of primitive and advanced traits helped to catapult Geoffroy into scholarly conflict with the reigning naturalist Georges Cuvier back in France and to establish Ètienne as a leading anatomist, embryologist and early evolutionary researcher of repute even today2. Now, on their own excursion under the very “evo-devo” flag that the discoverer of Polypterus helped raise, Canadian scientists Standen et al.3 suggest how the remarkable plasticity of the skeleton of Polypterus (the smaller west African relative of P. bichir, P. senegalus or “Cuvier’s bichir”) reveals a key part of the mechanism that might have facilitated the gradual transition from water to land and thus from “fishapods” to tetrapods (four-limbed vertebrates).

In a bold experiment, the authors raised 149 young bichirs on land and in water for eight months, then studied how they moved on land vs. in water, and also how the ultimate shape of the skeletal elements of the paired front fin bases differed between the land- and water-raised bichirs. Standen et al.3 discovered that both the form and function of the fins’ foundations transformed to better satisfy the constraints of moving on land. Land-acclimated bichirs took faster steps on land, their fins slipped across the substrate less, they held their fins closer to their body, their noses stayed more aloft and their tails undulated less, with less variable motions overall—behaviours that the authors had predicted should appear to enhance walking abilities on land. In turn, the bones of the neck and shoulder region altered their shape to produce a more mobile fin base with greater independence of fin from neck motion, along with improved bracing of the ventral “collarbone” region. These environmentally-induced traits should have fostered the locomotor changes observed in “terrestrialized” fish and aided the animals in resisting gravity, and they represent a common biological phenomenon termed developmental plasticity4,5. Interestingly, the land-reared fish could still swim about as well as the wholly aquatic cohort, so there was not a clear trade-off between being a good swimmer and a good walker, which is surprising.

Considered alone, the developmental plasticity of bichir form and function shows how impressive these amphibious fish are. But Standen et al.’s study3  ventured further, to apply the lessons learned from bichir ontogeny to a phylogenetic context and macroevolutionary question. The phenotypic plasticity during bichir development, they infer, could have been harnessed during the evolutionary transformation of fins for swimming into limbs for walking, in the “fishapod” ancestors of tetrapods. Indeed, bichirs are close to the base of the family tree of fishes6, and other living relatives of tetrapods have reduced or lost their fins (lungfishes) or adapted to strange deep-sea swimming lifestyles, never walking on land (coelacanths). Thus perhaps bichirs and the “fishapod” lineage share what Geoffroy would have called “unity of type”, today termed homology, of their developmental plasticity in response to a land environment. Surveying the fossil record of early “fishapods” and tetrapods, Standen et al.3 found that the macroevolutionary changes of neck and shoulder anatomy in these gradually more land-adapted animals parallel those they observed in terrestrialized Polypterus, providing ancillary support for their hypothesis.

A further test of the application of Polypterus’s plasticity to fossil tetrapods is naturally difficult. However, the “fishapod” lineage has some exceptional examples of fossil preservation. With sufficient sample sizes (e.g. fossil beds that reveal growth series, such as the Late Devonian Miguasha site in Canada7) and palaeoenvironmental gradients in fish or tetrapods, one could imagine performing a rigorous indirect test. Even small samples could be helpful– for example, the early tetrapod Ichthyostega exhibits some developmental changes in its forelimb suggesting that it became more terrestrial as it grew, whereas the related Acanthostega does not evidence such changes8— this hints at some developmental plasticity in the former animal.

During the Devonian period (~360-420 million years ago), were the “fishapod” ancestors of tetrapods floundering about on land now and then, gradually shifting from anatomy and behaviours that were more developmentally plastic (as in bichirs) to ones that were more canalized into the terrestrialized forms and functions that more land-adapted tetrapods retained? An attractive possibility is that the developmental plasticity could have led to fixation (reduction of plasticity), an evolutionary phenomenon called genetic assimilation, which another intellectual descendant of Geoffroy, Conrad Hal Waddington, promoted from the 1950s onwards9, a concept that now enjoys numerous cases of empirical support10 that this one may eventually join.

The nature of the genetic and developmental mechanism that bichirs use to achieve the observed developmental plasticity is still unclear. If it has a high enough degree of heritability, then it could be selected for in cross-generational experiments with bichirs. With sufficient time and luck raising these unusual fish, the hypothesis that their plastic response to a terrestrial environment can become genetically assimilated could be directly tested. This study could thus become an epic exemplar of how genetic assimilation can contribute not only to microevolutionary change but also to major macroevolutionary events, as was presciently suggested in a seminal review of developmental plasticity4.

This genetic assimilation is the Polypterus study’s reasonable speculation, and one that Geoffroy likely would have applauded, all the more for involving his beloved bichirs. Much as Napoleon’s landfall in Egypt was not a lasting success, bichirs never left wholly terrestrial descendants despite their malleable locomotor system. But the same type of plastic developmental mechanism that bichirs use today to make tentative, floppy incursions of the terrestrial realm might have been harnessed by our own “fishapod” forebears, leaving a far more revolutionary dynasty upon the Earth.

 

References

  1.  Geoffroy, E. (1802). Histoire naturelle et description anatomique d’un nouveau genre de poisson du Nil, nommé polyptère. Annales du Muséum d’Histoire Naturelle 1:57-68.
  2. Le Guyader, H., & Grene, M. (2004) Geoffroy Saint-Hilaire: A Visionary Naturalist. Univ. Chicago Press.
  3. Standen, E. M., Du, T. Y., & Larsson, H. C. E. (2014). Developmental plasticity and the origin of tetrapods. Nature, published online.
  4. West-Eberhard, M. J. (1989). Phenotypic plasticity and the origins of diversity. Annual Review of Ecology and Systematics 20:249-278.
  5. Pigliucci, M., Murren, C. J., & Schlichting, C. D. (2006). Phenotypic plasticity and evolution by genetic assimilation. Journal of Experimental Biology 209(12):2362-2367.
  6. Near, T. J., Dornburg, A., Tokita, M., Suzuki, D., Brandley, M. C., & Friedman, M. (2014). Boom and bust: ancient and recent diversification in bichirs (Polypteridae: Actinopterygii), a relictual lineage of ray‐finned fishes. Evolution 68:1014-1026.
  7. Cloutier, R. (2013). Great Canadian Lagerstätten 4. The Devonian Miguasha Biota (Québec): UNESCO World Heritage Site and a Time Capsule in the Early History of Vertebrates.Geoscience Canada40:149-163.
  8. Callier, V., Clack, J. A., & Ahlberg, P. E. (2009). Contrasting developmental trajectories in the earliest known tetrapod forelimbs.Science324:364-367.
  9. Waddington, C. H. (1953). Genetic assimilation of an acquired character. Evolution 7:118-126.
  10. Crispo, E. (2007). The Baldwin effect and genetic assimilation: revisiting two mechanisms of evolutionary change mediated by phenotypic plasticity. Evolution 61:2469-2479.

Read Full Post »

SupraHoloNet Transmission

Year 277 ABY, Fourth Imperial Age

Hoth System (location classified)

From: Dr. Zhonav Diphyryzas, Imperial Corps for Yesterday’s Misplaced Information; Knowledge Harvesters Unit; New Imperial Science Department

To: Dr. John of the Freezers, Unaligned World Contact #1314, Terran system

Subject: Functional Anatomy of Tatooine Megafauna

 

Dear Terran Science-Invigilator Dr. Freezers,

I write to you with the detailed correspondence I promised for your “blog carnival, whatever that is, and in honour of our Fourth Empire’s glorious leader Empress Syrrhosyx—may her inestimably wise and orderly rulership soon grace your distant world as it has our not-so-far-away galaxy. I hope that my Galactic translator continues to function properly with your crude technology. Our Empire’s embrace would grant your culture midi-chlorian-powered devices that would make our dialogue far simpler via intermental transmission, with minimal apparent side effects for you. You need not worry about the apocryphal stories that your people told about our first Imperial Age. That Skywalker kid was a terrorist, pure and simple. However, our inside sources reveal that the “documentary” in progress by the Terran named Jjabrams includes a rather accurate portrayal of the perfidious giant muromorph race from planet Dis’snai. “Baby steps”, as you say.

Our communications continue to be crippled by the mynock infestation that has plagued my orbital facility, and moreso by your own barbarian apparati. Thus the resolution of my images included here is a pale reflection of what our holo-imaging can achieve. But your readers can click the images to enhance their magnitude.

As the subject indicates, the transmission concerns my recent visit to the desert world of Tatooine, stimulated by investigations I conducted in the Corellian Science Museum. In that museum I found rare skeletal remains of the little-studied, reportedly extinct arthroreptile the Krayt Dragon (Tyrannodraconis tatooinensis by your archaic nomenclature). I’ll revisit this further below, because a subsequent discovery changed everything for me. I just wanted to whet your appetite, and this image of museum specimens of krayt dragons may do so:

Two fragmentary skeletons of small Krayt Dragons, from the Corellian Science Museum. (Image source here)

Two fragmentary skeletons of small Krayt Dragons, from the Corellian Science Museum. (Image source here) Note their short necks and quadrupedal limbs.

With growing fascination for the large land vertebratomorphs that are so startlingly diverse on Tatooine, I secured Imperial funding for an expedition to Tatooine, to survey the exotic megafauna and search for fossils of Tyrannodraconis that might further illuminate their evolution. My ensuing report summarizes my trilogy of investigations and discoveries from this “holiday in the suns”:

 

Stormtrooper on a Dewback in the Eastern Dune Sea (image source here).

Stormtrooper on a Dewback in the Eastern Dune Sea (image source here). Note how gracile the limbs are below the elbows/knees.

Investigation 1. Dissection of a Dewback, Mos Eisley

My ample funding (I’m sure you’re jealous) secured and stocked a laboratory for me in the colourful Mos Eisley spaceport, which has seen unprecedented commercial influx in recent years and now largely serves as an adventure park for hyperspace tourists (funded in part by the muromorphs of planet Dis’snai). With coliseum seating for a gathered host of some 1.6 million curiously slavering punters and drunken local yokels, I completed a full dissection of a fresh adult dewback (Iguanomorphus homoplasticus) specimen, illustrated below at its climax: exposure of the great fat body of the tail and the large caudofemoral muscle in the left thigh.  (curse this infernal Jawa 37C-H4 sketching droid’s malfunctions!)

Jawa 37C-H4 sketching droid illustration: My dissection of a common dewback, showing the caudofemoral muscle and tendon, tail fat body, and fibrous pads used while resting on the sand.

Jawa 37C-H4 sketching droid illustration: My dissection of a common dewback, showing (ventral view) the caudofemoral muscle and tendon, tail fat body (obscured by the nearby muscle), and fibrous pads used while resting on the sand.

My main observations support those of prior scholars, even from the Rebel Alliance era (bucking the trend of having to correct all their mistakes!): dewbacks have earned their moniker well by the characteristic water-condensing tissues on their dorsal surfaces. Microdroid explorations of these tissues, which lie within a dimpled midline ridge, house a high density of capillaries in a countercurrent network that surrounds a large number of specialised pores, or stomata, which smooth muscular rings contract to pull open when humidity, temperature and shade are best suited to cooling the surrounding air (via air currents encouraged by the stomata, and by local cooling via the capillary rete).

Previous scholars overlooked this mechanism, which conducts excessive warmth to the heat-emanative fat bodies in the bulky tail and the neck hump (my dissections nicely revealed these; similar tissues are concentrated in the foot pads and sternal pad). The mechanism also allows the body to be up to 20% cooler than the ambient air; an analogous adaptation to that seen in the banthas (below). My peers also failed to realize that the social nature of the dewback is key to its water conservation: while the stomatal rete can draw in some condensed water, it is far more effectively ingested by licking the backs of fellow dewbacks. Lone dewbacks thus are more prone to dehydration. The night-time group-huddling habits of dewbacks to conserve heat that they would otherwise too easily shed in the cool night air is yet another testament to the benefits of their sociality.

As ectotherms, dewbacks are slaves to the hot-cool cycles of the Tatooine wastes, but their sociality liberates them. Further escape comes from their large size (>800 kilograms of Terran mass units), which renders them mostly homeothermic, but never endothermic like some of your otherwise unimpressive Terran reptiles of past or present.

A laser-histology trek by microdroids showed the “scaled” hide around the rest of the body to be composed of siliceous material embedded in the thickly fibrous connective tissue of the skin, forming stereotyped arrowhead-shaped “siliceoderms”, as I term them, shown below.

Curious microstructure of the small "siliceoderms" from dewback skin that I have described-- single 'derm on the left, multiple 'derms surrounding a stomata on the right.

Curious microstructure of the small “siliceoderms” from dewback skin that I have described– single ‘derm on the left, multiple ‘derms surrounding a stoma on the right. To see these structures, one must view the “scales” at high magnification, ideally with microdroids.

I surmise that: (1) these siliceoderms are formed of fused Tatooine sand grains; (2) the grains become embedded into the soft, pliable skin as dewbacks grow, giving them insulation and physical protection; (3) young dewbacks display a previously mysterious behaviour of “sand-rolling” that encourages this embedding during the maturation of a dewback; and (4) the high strength and stiffness of this composite skin not only armours dewbacks but also pressurizes them, ensuring that blood can circulate through their large bodies without backflow or clotting issues, particularly in their gracile lower limbs, which are themselves passively supported by their skin tissues.

With your interest in animal locomotion, you may be curious about tales of how dewbacks can outrun landspeeders, especially in poor weather or terrain conditions. The skin-stiffening agents noted above surely play an important role in this. Indeed, much like your terrestrial varanid lizards, dewbacks do not follow the usual trend of straightening their limbs to support their body more effectively at larger body sizes (improving “effective mechanical advantage” as your field terms it), but they do draw them more closely under the body rather than remain sprawling. I revisit the matter of limb posture toward the end of my transmission.

Furthermore, the huge caudofemoral muscle shown above is able to transmit force from the tail to the thigh, and then its thick tendon transmits the force down the limb to the feet, acting as one strong limb extensor that powers and supports locomotion. No Terran animal does it so well. Banish any thoughts of how the dewback’s wrists and ankles seem implausibly thin– they are pressurized cylinders of dense tendon and bone, more like a Terran horse’s distal limbs than any lizard’s, and linked to far larger tail-to-thigh muscles. The expansive foot pads and reversed first toe (hallux; as in your Terran birds but with no association to arboreality) likewise give dewbacks a stable base of support and spread out their weight over the treacherous desert sands, reducing the work otherwise lost to deforming the sand’s surface and also keeping pressures on their feet at safe levels. Thus dewbacks have many features that explain their reputation for bursts of fast speed (~14 Terran meters/second or 50 kph/30 mph).

Yet whilst during the daytime and over short distances dewbacks can outpace banthas or humanoids on foot, their ectothermic nature causes them to accumulate fatigue too quickly, and thus they must rest. So sans cybernetic enhancements, dewbacks will never be winning any podraces. Nonetheless, I am sure you are awed by how Tatooine’s native reptiliforms, the dewbacks, exceed any living Terran reptile in their size and extreme adaptations to aridity. I have not even described the variations seen in feral, grizzled, cannibal or mountain dewback species, which can surpass the common desert dewback’s. Toward the end of my transmission I will show you animals that exceed even the greatest dinosaurs in sheer glory and ferocity.

Unlike the durable Tauntauns of my home system’s ice planet Hoth, however, dewbacks are ill-suited to cold climates because they are adapted to shed heat, not gain it. But the insulation of the next animal shows a more versatile performance…

 

Convincing image of a Bantha being ridden by a Sand-Person, from your world's fake documentary "Star Wars Episode IV: A New Hope", from Lucasfilm/Twentieth Century Fox.

Convincing image of a Bantha being ridden by a Tusken Raider/Sand-Person, from your world’s Rebel propaganda film “Star Wars Episode IV: A New Hope”, by Lucasfilm/Twentieth Century Fox.

Investigation 2. Field Dissection of a Bantha Bull

My anatomical study of a large male bantha (Megalingua feteoclunis) was hastened by not only the merciless heat but also by the imminent arrival of a horde of ravenous womp rats. Some quick incisions with my relict lightsaber sped my work. I focused my attention on three issues of scholarly interest: its marvellous tongue and glossopharyngeal adaptations (how does such a tall animal eat in a world that is far below it?), its hirsute integumentary system (what lies under that thick fur and how do banthas cope with the heat while wearing many wookies worth of wooly warmth?) and its peculiar, pillar-like limbs. The spiralling horns that add rings as the bantha grows, the nuchal ligament that supports the heavy head and neck, and the convoluted, multi-partitioned digestive tract that wrenches every last bit of nutrition from the lichens and other flora hidden beneath Tatooine sands are better understood. And with this bull I had no opportunity to study where the famous blue bantha milk comes from, but I have heard stories and no Terran mammal-esque udders are involved, let me tell you that much…

Anatomy of the oral apparatus of the Bantha, which I correct in my report although it is largely right (but how, Terran?). (source)

Anatomy of the oral apparatus of the Bantha, which I correct in my report although it is largely right (but how, Terran authors Terryl Whitlatch and Bob Carrau?). (source)

I don’t know how your Terran science-invigilators managed to get accurate information on bantha tongue anatomy (above) but I have to credit them, they almost got it right. With your can-do attitudes combined with your bungling mistakes, you’d make good Fourth Rebel Alliance members, but don’t get any new hopes. However, as the illustration below shows (and I had to leave the guts in the picture for their sheer impressiveness!), the tongue-projection mechanism extends not around the rear of the skull (occiput) and into the eyes or sinuses, but far back along the giant, spar-like breastbone (sternum) to the hips (pelvis, or propubis).

That mechanism’s powerful projection can extend the tongue as far as 3 Terran meters (10 feet). The tongue is expelled by stretching and then releasing (slowly for precise control, or quickly for a catapult action) a fibrous sac that surrounds the base of the tongue, and this sac then recoils elastically when released to withdraw the tongue. I’ve studied your Terran elephant and chameleon and it combines aspects of both of these, with the tongue having several layers of fine muscle fibres as in the former animal, and the “power amplifier” catch mechanism of the latter, thus providing a superior combination of control and speed. All of these are rightly called muscular hydrostats, but the bantha’s is the best.  You might mention your Terran pangolin as a counter-example, but does that little creature have the spiracle-bearing, ultrasensitive chemosensory tongue and majestic size of the bantha? No. I rest my case.

Jawa 37C-H4 sketching droid illustration: My dissection of a bantha, showing the tongue attachments (note the distal bifurcation), digestive tract and foot structure. The colour variations in the digestive tract seem to be produced by commensal arthroreptiles.

Jawa 37C-H4 sketching droid illustration: My dissection of a bantha, showing the tongue attachments (note the distal bifurcation), digestive tract and foot structure. The colour variations in the digestive tract seem to be produced by commensal arthroreptiles.

A naïve Terran like yourself might wonder why, of all things, a giant desert mammal such as the bantha would evolve to be clothed in thick fur. Here you would reveal your feeble way of grasping about the diversity of pangalactic Nature. First of all, banthas are not mammals as you know them; a Terran word like pseudomammal would suffice. They lack the diagnostic traits of mammary glands, true hair, and inner ear bones that diagnose the Mammalia of your homeworld, but evolution at a giant size in a hot, dry clime has chastened them to become at least superficially similar to a Terran mammal such as an elephant or mammoth. One might be so naïve, even, to think that a bantha is merely a proboscidean in hairy disguise, but drive such thoughts from your rickety cerebral-implant-deprived mind.

Behold, the true nature of bantha fur, as I have seen with microdroid holo-imaging: it is a second, external circulatory system of sorts. Simply put, the hairs have a thermo-conductive submolecular structure that deflects heat (and even, to a degree, the energy of a blaster) and traps cooler air near the body with an intricate network of cross-linking of barbed fibers more like a Terran bird’s feathers than mammalian hair. In this cooler locale, tracts of spongy skin tissue collect condensed water and direct it to absorbent epithelial beds on the chin and lips, belly, and toes, where the bantha imbibes it, or simply sheds it off to carry further heat away. Thus here we have a fascinating case of convergent evolution with the reptiliform dewbacks, but surpassing even that animal’s adaptation and evolving what you would likely call an air-conditioning system. Banthas cool themselves by circulating a slick of cool water around their body inside a heat-resistant fluffy outer mesh. Whether their horn tissues or tails contribute to this system is yet to be investigated.

Lastly, I have conducted holo-viewings of the biomechanics of bantha gaits from numerous remote studies of wild and Sand People-ridden animals, in light of my own dissections of this bull. What strikes me is the phenomenal convergence with giant quadrupeds on your homeworld: like sauropods, elephants and other species, banthas have evolved “graviportal” or weight-bearing adaptations: (1) limbs that are proportionately longest above the elbow and knee, not distally elongated as in “cursorial” animals; (2) heavy, robust bones that lack much of a marrow space; (3) short, thickly padded feet ending in bulky claws or hooves (three toes in the case of banthas); (4) an emphasis on lateral sequence (left hind-left front-right hind-right front) footfalls when walking, extended to a slightly bouncing, rolling “amble” at faster speeds; (5) strongly vertical limbs when walking, using the limbs more like pillars to support the weight more effectively; and (6) slow maximal speeds, limited to ~7 Terran meters/second (24 kph/15mph) at best.

At around 4000 kg of typical body mass, banthas overlap with the masses of your planet’s erstwhile giants that have such features. I did not uncover any “predigits” supporting the feet of banthas as you had in elephants; rather, their “heels” involve dense fibro-elastic cartilage, which works analogously to give shock-absorbing and resilient properties to the feet. This suite of graviportal features reinforces an idea that is now recognized pan-galactically: At huge sizes, land animals must act relatively more constrained by gravity, becoming forced to adapt more aspects of their biology to resist its pull, lest they strain muscles, break bones, snap tendons, or fall and injure themselves. Thus the convergent evolution of banthas and elephants is no surprise. But is there another way to be an imposing giant? Perhaps…

 

Investigation 3. On some remains of the “extinct” Krayt Dragon

Ever since I left my home system, thoughts kept tumbling through my mind like rocks in an asteroid field, concerning the krayt dragon bones I had viewed in the museum on Corellia. With the krayt (Tyrannodraconis sp.) lineage reported extinct since at least the year 22 ABY, following much publicity of its awesome nature, its menace seemed now but a phantom. Consequently I could only fantasize of deeper study. That is, until a rumour came to me while resupplying in the well-preserved city of Bestine: not far off on the edge of the Jundland Wastes, a stormtrooper patrol had taken down a strange, enormous, multi-legged arthroreptile that had gone after their dewback mounts. A quick skyhopper flight and I was there, giddy with the adrenaline of impending discovery.

Another Terran artist renders a compelling illustration, of a Greater Krayt Dragon in life. Where indeed do they get their information from? Bothan spies, I suspect. (Source)

Another Terran artist (one of Terryl Whitlatch and Bob Carrau) renders a compelling illustration, of a Greater Krayt Dragon in life. Where indeed do they get their information from? Bothan spies, I suspect. (Source)

It was a magnificent carcass. Sandworms and scurriers were already attempting to scavenge it, but with little luck and easily driven off with a few shots from my carbine. No stormtroopers remained (alive, anyway), so I didn’t get any details of the fracas that led to this well-timed demise, but the blast points on its body were too precise for sandpeople, and characteristic dewback tracks were everywhere. Even my antique lightsaber seemed poorly up to the task of dissecting this titan: it was over 30 meters (100 feet) long and surely 100 tons of Terran mass if not more; on the scale of your sauropods, but so vastly different in other ways. Right away, from its tracks I could see it had a peculiar mode of movement in life: it had slid up to some rocky cover in these badlands, dragging its belly and bulk along with ten limbs that were slender in comparison to its body, but still each as big as a large bantha’s. I took a deep breath and cut into what was the first Greater Krayt Dragon seen in some 255 years.

Jawa 37C-H4 sketching droid illustration: My dissection of the Greater Krayt Dragon, to extract the Dragon Pearl. The stormtrooper shown forgot the tale that Krayts take 1 hour to die, and so got too close too soon.

Jawa 37C-H4 sketching droid illustration: My dissection of the Greater Krayt Dragon, to extract the Dragon Pearl. The stormtrooper shown forgot the tale that Krayts take 1 hour to die, and so got too close too soon.

If the bantha dissection was a rush job, this one was a sprint. Pockets of gas were forming and erupting while I sliced my way toward the bones and other organs of most interest, with the forces of decomposition slowly winning a race against my science. Oh, if only I’d had a Jawa sandcrawler to repurpose as a mobile freezer! And the sandworms and scurriers were still lurking about, with far nastier things surely soon to be drawn by the carnage out in these remote wastes. Those two days blurred exhaustion and inquiry and disgust and elation into a mire in my mind more pernicious than any on Dagobah. I’m no longer sure of what I saw– you’re probably wondering if I found the fabled krayt dragon pearl in the gizzard, and yes, there was one but I lost it somehow. Same with the venom sacs. Maybe I sipped from one of those; that would explain a lot. I made a sketch that I reproduce here, but then in a crazed, diaphonic state of dehydration and euphoria and frustration I am pretty sure I cut my sketching droid to pieces too, so this is all that remains to bolster my frazzled memories.

Now that I’ve recovered and ruminated, I have come to some conclusions. First, I am left doubting all the little we know about krayt dragons. It is said that they existed in canyon, normal and greater species, and the immense variation of curved horns, clawed limbs and flanged tails lent this taxonomy much credibility in the past. But, call it chronic heatstroke or inspiration as you may, what if all krayt “species” are just stages of a long and repeatedly metamorphic developmental sequence? As my graph below shows, and this is admittedly pieced together from what few museum specimens and documents I have since marshalled to test my hypothesis, krayt traits change uniformly with their body size. As they get bigger, krayt dragons get more multi-legged and longer-necked, diverging from the form of their relatives (in the evolutionary sense of your sciences, sister group or outgroup) from Ruutan, the Kell dragons. The genus Tyrannodraconis, more so than the Kell, betrays its arthroreptile ancestry with their spines, exoskeletal plates, and tendency for polypedality. Their sternum also elongates to support their chest as they change from lumbering, bantha-chasing quadrupeds to slithering, sarlacc-snatching octa- or decapedal behemoths.

Although based on little concrete data, my analysis of known Krayt and related specimens suggests that they change continuously during ontogeny, although leg number may shift more suddenly (I predict this happens during their first metamorphosis at sexual maturity). Strong allometric scaling of neck and total length is evident- if the two lengths scaled as mass^0.33 they would be maintaining shape across the proposed growth series. But they don't.

Although based on little concrete data, my analysis of known Krayt and related specimens suggests that they change continuously during ontogeny, although leg number may shift more suddenly (I predict this happens during their first metamorphosis at sexual maturity). Strong allometric scaling of neck and total length is evident- if the two lengths scaled as body mass0.33 they would be maintaining shape across the proposed growth series. But they don’t.

I return to the best-documented krayt dragon remains: those that even Terrans have seen in the Rebel propaganda film you call “Episode IV”. Dr. Freezers, even your fellow blog-invigilators at SV-POW! discussed it. Witness the large size and long neck of the typical Krayt; whether horns existed or not in that form from the film is uncertain, and I note that these could even be a sexually dimorphic feature, but this is beside the point. Remnants of the body and limbs were never found. But this specimen fits well with my idea that all krayts are one species, or two at most—and how many top predatory megafaunal species could coexist on a desolate arid planet like Tatooine anyway?

What still strikes me is the phenotypic variation in krayts: some large or small varieties have from two to four toes, and different scythe-like horns on their tail tips. This leads me to heap speculation atop my precarious pile of hypotheses: what if krayts are simply phenotypically labile, varying their traits almost stochastically between individuals due to relatively flexible ontogenetic programming, but still following strong overall trends as size increase, like those I have plotted above? Those stronger trends might be more tightly regulated by homeobox-like genes similar to those that have shaped so much of your Terran metazoan diversity, influencing features along the body axis like those I have mentioned (neck, limbs) across growth? I like this idea too much for it to be true, I admit. But if one krayt dragon existed just a short time ago, it is not simply fodder for the cryptoxenozoologists. And so, sooner or later, someone will answer my scientific salvo. I predict that burrows where the krayt dragons metamorphose between life stages, growing new legs and longer bodies, will be found in due time.

However, I have a stronger inference that I present to you as part of our common interest. On Terra and Tatooine alike, larger animals tend to adopt more straight-legged limb poses to improve their leverage, as I outlined with the dewbacks above. I plot existing data for Terran animals with my best estimates (for dewbacks and banthas, quite reliable; for krayts, my guesses) for this “effective mechanical advantage” below. What this shows is that dewbacks and Banthas both fall below the “normal” curve for Terran land mammals, as I explain:

In the case of dewbacks, this decrease of limb leverage seems offset by passive support from their pressurized scaly legs and enlarged whole-limb extensor muscles of their hindlegs, so they are overall about as well adapted to bursts of speed as large mammals from your world, such as buffalo or large antelope, even if their endurance suffers (a tradeoff, perhaps, for their reptile-like adaptations to desert life).

In the case of banthas, they do no better or worse than elephants; all are slow due to their size and “graviportal” focus of adaptations. Like elephants, but unlike dewbacks, banthas do not “invest” more body mass into supportive leg muscle, and so they are slower than they might otherwise be.

Effective mechanical advantage of the limbs, with Terran data for mammals (red+blue) (source 1 and source 2), and my new data for Tatooine megafauna. Past a moderate size, EMA either declines or remains constant. Once the limbs are fairly straight (near the size of a Terran horse), EMA cannot be much improved.

Effective mechanical advantage (EMA) of the limbs, with Terran data for mammals (red+blue) (source 1 and source 2), and my new data for Tatooine megafauna (green). Past a moderate size, EMA either declines or remains constant. Once the limbs are fairly straight (near the size of a Terran horse, or Tatooine eopie; vertical dashed line), EMA cannot be much improved.

But the krayts (young or smaller species aside) suffer more from their size than other Tatooine megafauna, as they do not increase their limbs’ mechanical advantage any more than the others do, and so they must become slower as they grow. This explains, however, why their ecology shifts from being a mobile predator when smaller (feeding on dewback, then bantha-sized prey) to being more of an ambush predator or specialist on slow/immobile prey like sarlaccs as they attain titanic sizes. Their limbs, despite becoming more numerous, must become less able to support them as size increases, as in other Terran and Tatooine megafauna, and thus they are destined to benefit from giant size (in many ways, including near-invulnerability and capacity to take the largest prey) at a cost of athleticism (but with prey like sarlaccs, who needs it?). In the greater, or fully mature, krayt dragons, I suggest that the limbs each become less supportive and more of a stabilizer to prevent their slug-like bulk from rolling over, or a set of “oars” to help them navigate through sandy environments like the Dune Seas. They support their weight not so much with limbs and levers, but with a larger, cuirass-like breastbone system, rings of muscles and fibrous tissue, and their whole elongate body.

The ultimate implications of my biomechanical research are summarized below—I am sure you will agree with my reasoning.

Maximal speed vs. body mass data from (black) Terran animals (source), and (green) Tatooine megafauna (plus non-native Kell dragons for comparison). As size increases past ~100 kg mass, speed inevitably declines.

Maximal speed vs. body mass data from (black) Terran animals (source), and (green) Tatooine megafauna (plus non-native Kell dragons for comparison). As size increases past ~100 kg mass (when EMA in the other graph above is already maximal), speed inevitably declines.

As for those that have said that Greater Krayt Dragons and such are thereby confined to a life as scavengers and nothing more, I would welcome them to explore the Jundland Wastes locales armoured by all the security that this foolish notion provides. I, for one, would enjoy viewing such a visit, but only remotely via a probe droid’s holo-feed.

One of your Terran artists (jeddbub on deviantart) produced a provocative imagining of a Greater Krayt Dragon facing a Jedi. I'd wager for the former.

One of your Terran artists (jeddibub on deviantart) produced a provocative imagining of a Greater Krayt Dragon facing a Jedi. I’d wager for the former.

I submit this report in honour of Empress Syrrhosyx and the Fourth Empire– may you find the contents enlightening and may her rule grace your benighted homeworld before you, too, have nothing left of your megafauna but stories of dragons.

I welcome your comments, and perhaps some of your lauded “freezerinos” would care to comment below—but they must behave themselves, lest I find cause to deposit them in carbonite for hyperspace shipping to a lonely suffering on a lonely planet!

I shall shortly return this “blog” to your control, when the mood strikes me. That is the deal for this correspondence. Pray I don’t alter it any further.

Enjoy your little blog carnival, Terrans…

Pangalactically,

Dr. Zhonav Diphyryzas

Read Full Post »

Older Posts »

Follow

Get every new post delivered to your Inbox.

Join 3,263 other followers